Beyond Acute Overdoses: A Case of Chronic Clozapine Toxicity With Non-specific Presentation.

Clozapine is recognized as the gold standard for treating treatment-resistant schizophrenia but carries a notable risk of severe adverse effects. This case report presents a 61-year-old Welsh woman with paranoid schizophrenia and epilepsy who, while on long-term clozapine and valproic acid therapy, developed a progressive decline in mobility, cognition, and social engagement, punctuated by recurrent falls. Despite numerous hospital visits and extensive investigations, the underlying cause of her symptoms remained elusive until serum clozapine level testing revealed toxicity, with levels significantly exceeding the therapeutic range. Following the gradual tapering and ultimate cessation of clozapine, the patient exhibited marked improvements in both mobility and cognitive function. This case highlights the potential utility of serum level monitoring in patients on clozapine, especially those showing unexplained deterioration in mobility and social engagement, as toxicity can arise even after prolonged stable treatment. The findings emphasize the necessity for vigilant monitoring and proactive management strategies to mitigate the risk of severe neurological complications associated with clozapine therapy.